What is this stuff?

udidwht wrote:
I have a newer Dometic RM 8501 and it drains into a small drip cup/tray.

That is because the design of the outside doors. Doug

I have a newer Dometic RM 8501 and it drains into a small drip cup/tray.

Dometics are NOT supposed to drain to the back of the refer. They are either installed poking out the lower door holes or secured to the outer lip just behind the access door to drain down the side of the RV. Also, the original drain hose is about 3 foot long with more than enough to loop and then install on the correct exit. If yours was shorter it was because the installers cut off the excess as they did not know the correct install as I mentioned. Norcolds drain into a cup mounted beside the LP burner flue to evaporate any liquid and also the Norcolds have a check valve on the end.

^ Yeh, they usually just drain inside the back of the fridge.

Typically, there's not more than a few drops of water produced - if any.

On my 2016 Newmar Bay Star Sport the refer drain line has one of the plugs noted above. It is however siliconed to the cabinet floor inside the cover, not through the grill.

Sorry I wasn't clear...the original line broke from brittleness and was TOO SHORT to exit through the vent baffle and so was dripping inside the fridge compartment. The end plug was long gone along with the broken end. I replaced the line and added the plug you linked to. Although it's hard to digest the price of that little thing, no bigger than a dime.

My guess was also some kind of insect detritus, I just had never seen anything like and wondered if anybody had. Thankfully fridge is working great, although it hasn't been too hot outside.

From the color, I would say Dometic refer. I think it is some type of insect debris/nest. Also, the original line was NOT too long. The reason it was that length is, it is supposed to be installed with a loop to prevent air migration back up. I will bet in 43 years as a Tech, I have seen maybe 4 or 5 installed correctly in thousands of refers I have worked on. Also, the end of that original tube should have a plug in the end with small holes to prevent insect migration. Holes just large enough to allow water drip out. Also, when you use the drain line you stick it one of the outside lower access door vent holes to allow the water to drain to the outside. Doug

This link shows that plug

https://getrvparts.com/dometic-2932115013-rv-refrigerator-drain-hose-tube-plug-cap/

Something to let the water through, but keep the bugs out? Rather than a screen on the end?

Cellulose?